1. Field of the Invention
This invention relates to propelling gas systems for aerosol products.
2. Description of the Prior Art
Many products designed for household, personal or industrial use are available as aerosol products. Typical examples of such products and ones in which the propellant system of the present invention can be used include personal products such as hair sprays; household products such as paint removers and insecticides; industrial products such as penetrating oils and metal-cleaning sprays; and agricultural products such as tick and flea repellants. All such products utilize the pressure of a propellant gas or a mixture of propellant gases (i.e., a propellant gas system) to expel the active ingredients from the container. For this purpose, most aerosols employ liquified gases which vaporize and provide the pressure to propel the active ingredients when the valve on the aerosol container is pressed open.
An important physical property associated with the dispensing of aerosol products is the vapor pressure of the propellant. Vapor pressure from the viewpoint of this invention is the pressure exerted when a liquified propellant gas is in equilibrium with its vapor in a closed container, such as an aerosol can. Vapor pressure can be measured by connecting a pressure gauge to the valve on an aerosol can or gas cylinder containing the vapor/liquid mixture. A standard of measurement of vapor pressure in the U.S. aerosol industry is pounds per square inch gauge (psig) with the gas/liquid mixture at constant temperature, most commonly at 70.degree. F. When vapor pressure is mentioned in the ensuing specification without reference to temperature, it can be assumed that the pressure is determined at 70.degree. F. The vapor pressures of liquified gases most widely employed as aerosol propellants will vary over the range of about 20 to 90 psig at 70.degree. F. However, for a great many aerosol products, propellants with a vapor pressure in the range of about 50 to 60 psig are most desirable. The propellant systems of the present invention have vapor pressures in this latter range.